docs: def polyfit(self, sampled):
          """
          Compute Chebyshev coefficients for values located on Chebyshev points.
          sampled: array; first dimension is number of Chebyshev points
          """
          asampled = np.asarray(sampled)
          if len(asampled) == 1:
              return asampled
          evened = even_data(asampled)
          coeffs = dct(evened)
          return coeffs